Ajax on backend

I am trying to save & update custom theme options using ajax to prevent page reload. but ajax always return 0 although I am using die() at the end of the code.

function.php code

wp_enqueue_script( 'fw_js', get_template_directory_uri() . '/core/framework/js/script.js', array('jquery'));
wp_localize_script( 'fw_js', 'shark_ajax', array( 'ajaxurl' => admin_url( 'admin-ajax.php' )));

ajax code

jQuery('#zmfw_update_options').click(function(s){
s.preventDefault();
window.zmfw_options = jQuery('#shark-options-form').serialize();
jQuery.ajax({
type: 'POST',
url: shark_ajax.ajaxurl,
data: {
action: 'zmfw_shark_ajax',
optdata: 'iam aher'
},
success: function(data){alert(data);console.log(data);}
})// end ajax
})//end update_options click function

Process_options.php code

<?php
add_action('wp_ajax_zmfw_zmfw_shark_ajax', 'zmfw_shark_ajax');
add_action('wp_ajax_nopriv_zmfw_shark_ajax', 'zmfw_shark_ajax');
add_action( 'wp_ajax_zmfw_shark_ajax', 'zmfw_shark_ajax' );

function zmfw_shark_ajax (){
$update = update_option('zmfw_shark_options', $_POST['optdata']);
$retrive = get_option('zmfw_shark_options');
die($retrive);
}
?>